It is known to implant an artificial/prosthetic ligament to replace a natural ligament which has become damaged. Conventional artificial ligaments are formed from strands or bundles of artificial fibres which may be woven and/or aligned to form a flexible member which is substantially uniform in size and is resilient along its length.
A natural ligament exhibits high strength, toughness and resilience and retains these properties for many years. To date, it has been impossible to match these properties using artificial fibres.
When implanted, artificial ligaments can be attached to existing bone tissue as long as the attachment site is relatively intact. However, if surrounding bone tissue is significantly diseased or damaged, it may be necessary to remove both the natural ligament and the adjacent bone tissue and replace them with prosthetic components. In severe cases of disease or damage, the natural joint may be replaced with a total joint replacement prosthesis.
When implanting a total joint replacement prosthesis, both cruciate ligaments are often lost. The functionality of the ligaments must then be replicated as closely as possible by one or more features of the replacement prosthesis (as for example in the case of a cooperating cam and post in a total knee replacement). However, it has proved extremely difficult to replicate the natural kinematics of a joint without the presence of naturally functioning ligaments. This is particularly evident in the case of the knee joint, which exhibits a complex movement that is highly dependent upon the interaction of ligaments with the articulating areas of bone.
Joint replacement prostheses commonly comprise two bone engaging components that articulate via a bearing component. In a total knee replacement prosthesis, the bone engaging components are a femoral component, comprising an anterior surface with patella track and two femoral condyles, and a tibial component, comprising a substantially planar surface or tray and a post, keel or other stabilising feature. The femoral and tibial components articulate via a bearing component mounted on the tray of the tibial component. The bearing component may be fully or partially fixed with respect to the tibial component, and commonly comprises a single piece of high density polyethylene.
In order to more closely replicate the natural kinematics of the knee, it is desirable for a total knee replacement prosthesis to facilitate a combination of rolling, rotational and translational movement between the femoral and tibial components of the prosthesis. This can be achieved in part by employing a “mobile” bearing component, having some freedom of movement relative to the tibial component on which it is supported. In addition, it has been shown that mobile bearing components exhibit more favourable wear characteristics than so called “fixed” meniscal bearings.
When the wear in the knee joint is limited to only one medial or lateral compartment, it is known to replace only the bearing surface of the femoral condyle and the cooperating portion of the tibia of that compartment with a partial or “uni-compartmental” joint replacement prosthesis. Particularly where such a prosthesis uses a mobile bearing, there will be an increased risk of dislocation in the event of joint distraction, if one or more of the ligaments of the knee are diseased or otherwise damaged. With this in mind, it would be very advantageous to be able to implant an artificial/prosthetic ligament during the joint replacement procedure to restore full stability and maintain natural joint articulation.